This invention relates to Versa-Module European (VME) Extensions for Instrumentation (VXI) based systems and products, and in particular, to an apparatus and method for configuring a VXI product plug-in to increase product component density, to an apparatus and method for facilitating the insertion and removal of VXI product carriers into and out of a standard VXI chassis, to an apparatus and method for facilitating the interfacing of new VXI products with a controller of VXI backplane systems, to an apparatus and method for providing an internal bus for selectively coupling VXI product modules, to a method and apparatus for providing an emergency reset mechanism to protect VXI product modules individually or together from potentially hazardous conditions, and to a method and apparatus for providing electromagnetic shielding between VXI product modules.
The VXI bus is a standard computer interface bus that originated in Europe, but has been widely accepted around the World. Its primary use has been in the testing and diagnostic field. For instance, it has been used for testing and troubleshooting of automobile components, medical devices such as pacemakers, computer-based systems, and microprocessor integrated circuits. Because of their testing and diagnostic capabilities, VXI bus systems typically comprise a plurality of switching modules. These switching modules connect to a unit-under-test (UUT) for testing and diagnostic purposes. A computer controller interfaces with the VXI backplane system to operate the switch modules in accordance with a testing and diagnostic strategy.
The VXI standard includes numerous specification requirements. These specifications include, for example, chassis size and configuration requirements, power requirements, cooling requirements, backplane protocol requirements, and connector requirements, to name a few. Typically, designers of VXI products must adhere strictly to the required specifications of the VXI backplane system. Of particular interest to the invention is the VXI chassis slot configuration requirements.
FIG. 1 illustrates a simplified representation of the front face of a standard VXI chassis 100 of a VXI based system that is used in the prior art. The standard VXI chassis 100 includes a plurality of standard size slots 102 for respectively receiving therein VXI product plug-in 104 that connect to a VXI backplane bus situated at the back of the chassis (not shown in FIG. 1). FIG. 1 illustrates a representative sample of two (2) adjacent slots 102 for housing therein two adjacent VXI product plug-ins 104. A computer (not shown) can communicate with the VXI product plug-ins 104 by way of the VXI backplane bus through the use of a standard connector 106 located on an adapter module 107 typically positioned within the left-most slot of the chassis 100. The VXI product plug-ins 104 each include a housing 108 that is sized and dimensioned to slide into respective slots 102. A module card 110 is contained within each of the housings 108 for performing particular programmable functions. These modules may perform many types of operations, but for the purpose of this application, switch modules will serve to illustrate the invention.
As previously discussed, there are standard size and configuration specifications for the VXI chassis 100. One of the specifications include slot width and length requirements. Thus, designers of VXI products typically design a plug-in so that it is sized and dimensioned to slide into one of these standardized slots. Accordingly, a VXI product designer is somewhat restricted as to the available area for implementing the desired function(s) for the VXI product plug-in. This typically limits the number of components that can be incorporated into a plug-in. If the products are programmable switching networks, the slot size requirements may limit the number of switches that can be incorporated into a VXI product plug-in.
FIG. 2 illustrates a block diagram of a prior art VXI based system 120 including a pair of VXI switching product plug-ins 130 and 132 positioned within respective VXI chassis slots (not shown in FIG. 2) and connected to a VXI backplane bus 142. The VXI switching plug-ins 130 and 132 include respective carrier housings 134 and 136 (represented by a dashed box) that houses respective pairs of switch cards 138 and 140. The switching cards 138 and 140 include respective connectors situated at the back side of the carriers in a manner that when the plug-ins are slid into corresponding slots of the VXI chassis, the connectors make operational contact with corresponding connectors on the VXI backplane bus 142. As it is typical of a VXI bus configuration, it includes lines for supplying power, lines for providing VXI signals, and non-designated lines for custom usage by a designer. The non-designated lines of a VXI backplane bus 142 are typically referred to as the local bus, and will be abbreviated herein as xe2x80x9cLBUS.xe2x80x9d
Each of the prior art switch module cards 138 and 140 include a plurality of functional circuitry. For instance, they include respective address selector switches and associated circuitry so that the switch modules are separately identified. They also each include a VXI signal decoding circuit for interpreting the commands received from the LBUS. In addition, they each include a differential driver receiver, which is required for receiving the signals from the LBUS. The local bus LBUS comprises a plurality of non-connected segments which may be connected respectively to each of the switching modules. The switching modules each include LBUS Jumper switches in order to cascade or daisy-chain the switching modules. In the diagram shown in FIG. 2, the LBUS jumper switches when set connects LBUS IN to LBUS OUT. Each switching module includes a switching bank, typically made of an array of relays and associated interfacing circuitry.
At least one of the switch modules incorporated into the VXI based system 120 should include a controller circuit, such as controller circuit 144 present in switch module 138. The controller circuit receives the commands or VXI bus signals from the VXI backplane bus 142, and decodes these signals in order to issue address and data information for all of the modules connected to the LBUS. The address and data information issued by the controller 144 are directly applied to the switch module 138 card that incorporates the controller, or indirectly to the other modules, such as module 140, through the LBUS, which may be cascaded or daisy-chained as previously discussed. If all the modules are cascaded in the VXI based system, every module will receive the address and data information issued by the controller, and the addressed module or modules will respond accordingly.
Referring now to both FIGS. 1 and 2, the prior art VXI based system does not utilize the available slot area of the VXI chassis 100 in the most efficient manner. For instance, each adjacent pair of plug-ins in the system has an unavailable or wasted region 112 between adjacent plug-ins 104 (shown much larger than it really is for the sake of viewing). In addition, there is substantial unnecessary redundancy in each of the switching cards 138 and 140 by the inclusion in each of the cards an address range switch, VXI signal decoding circuit, a differential driver receiver, a power filtering circuit, and LBUS jumper switches, which would not be duplicated if the modules were in one integral package. With this unnecessary redundancy, existing prior art switch modules are limited to switching banks of approximately 160 switching relays. Thus, a total of about 320 switching relays can be accommodated by two adjacent slots 102. Currently, there is a demand for more relays within that space.
Thus, there is a need to reconfigure the existing design of the prior art VXI based system to reduce the amount of wasted space and unnecessary circuit redundancy so that a higher density of components, such as switching relays, can be achieved within the size parameters specified for the standard VXI chassis.
There are additional needs for providing a higher component density for the available slot size. These needs include facilitating the insertion and removal of VXI product plug-ins into and out-of a standard VXI chassis, facilitating the interfacing of new VXI products with controllers of existing VXI based systems, providing a programmable internal bus for selectively coupling VXI product modules, providing an emergency reset mechanism to protect VXI product modules individually or together from potentially hazard conditions, and providing electromagnetic shielding between VXI submodules that occupy the same VXI bus module.
One general objective of the invention is to provide more components within the existing parameters of a VXI based system. If the VXI based systems and products are used for testing and diagnostic applications, where the product plug-ins are primarily switch cards, then it is an objective of the invention to provide more switching components per a given area allotted in a standard VXI based system. An apparatus and method is provided herein for accomplishing these objectives. The concept involves providing a VXI product plug-in module that is sized and dimensioned to occupy two adjacent standard size slots in a standard VXI chassis. By doing so, the VXI product plug-in takes advantage of the wasted space between two adjacent single-slot plug-ins that would be undesirably present in a prior art VXI based system.
More specifically, the VXI product plug-in in accordance with the invention comprises a carrier housing partitioned into a front compartment and a rear compartment. The front compartment is further partitioned into an upper sub-compartment and a lower sub-compartment. Both of the upper and lower sub-compartments are preferably configured to house three horizontally-stacked module cards. Thus, for a two standard size slot area, the VXI product plug-in of the invention provides six module cards. In the present design, one of these module cards can house a bank of 80 switching relays, in the case where the module card is of a switching type. Since there is space for six switch modules for each plug-in, a total of 480 switching relays can be provided within two adjacent standard size slots of a standard VXI chassis. Whereas, in the prior art VXI based system, two prior art VXI switching plug-ins situated within two adjacent standard size slots, can house a total of 320 switching relays (160 switching relays per prior art plug-in). Thus, the VXI product plug-in of the invention provides a 50 percent increase in the switching relay density over that of the prior art plug-in. This is a substantial advantage since there is a demand for higher component density for VXI based systems and products.
Since a plurality of the modules, preferably six, are housed within compartments of the VXI plug-in carrier housing, there is a need to provide electromagnetic isolation between the modules to prevent interference or cross-talk between the modules. Accordingly, a thin sheet of electrically conducting material is provided between adjacent modules that preferably extends throughout the board length and height of the module. The thin conductive sheet is connected to a grounding plane on an internal backplane of the plug-in.
The rear compartment of the plug-in carrier in accordance with the invention houses a circuit for interfacing a VXI backplane bus with the modules occupying the front compartment of the carrier. Specifically, the interfacing circuit preferably comprises a mezzanine board, a bridge board, and optionally a controller board. More specifically, the mezzanine board interfaces with the VXI backplane bus to provide filtering of the VXI bus power lines and to provide these lines to the switch modules and the controller card. The controller card interfaces with the VXI backplane bus in order to decode or interpret data received from the VXI bus along the VXI signal lines, and to issue address and data information that are provided to the VXI modules along the local bus (LBUS) of the VXI backplane bus. The controller card has the capability of operating in a message based mode, using for example the IEEE 488.2 protocol or the Small Computer Programming Instruction (SCPI) protocol. In addition, the controller card has the capability of operating in a register based mode for increase throughput.
The bridge board interfaces with the VXI backplane bus to receive the address and data information issued by the controller card along the local bus (LBUS) of the VXI bus, and issues address, data and handshake signals for the six (6) VXI modules in data communication with the corresponding bridge card. A VXI based system need only have one plug-in that incorporates the controller card. The other plug-ins of the system can receive the addressing and operating instructions from the controller board by way of the local bus (LBUS), which can be configured in a daisy-chain manner for providing a connection between the controller card and potentially all the plug-ins sharing the VXI bus.
The VXI plug-in of the invention further includes an internal backplane bus that is preferably situated within the carrier between the front and rear compartments. It provides an interface between the mezzanine and bridge boards occupying the rear compartment, and the switch modules occupying the front compartment of the carrier. The internal backplane bus includes power busses that interface with the power lines of the mezzanine and bridge boards, and power lines of the switch modules. In addition, the internal backplane includes a programmable bus, referred to herein as the analog bus, configured in accordance with an aspect of the invention so that the six modules can be selectively coupled together in many combinations. In the preferred embodiment, the analog bus includes six module interfaces that are cascaded together by four independent differential signal busses. Each segment of the independent differential bus that couples adjacent module interfaces includes a series-connected relay switch housed by each of the six modules for selectively coupling the adjacent module interfaces. The relays can be set in a particular manner so that a desired connection is made between two or more selected modules.
Another aspect of the invention is to provide a mechanism for facilitating the insertion and removal of the VXI product plug-in card to and from the VXI chassis. This is accomplished by a pair of injection/ejection mechanisms that are pivotably coupled to the top and bottom of the carrier housing. The injection/ejection mechanism preferably includes a handle integrally attached to a pivot member having a bulb-shaped opening or hole centered at the pivot point and sized and dimensioned to receive a pin or the like to pivotably mount the mechanism to a carrier member. The pivot member includes an injection and ejection protrusion configured to contact a frame structure of the standard VXI chassis (designated herein as a xe2x80x9ccard guide railxe2x80x9d) during the operation of the mechanism. During insertion of the plug-in into the VXI chassis, when the plug-in connectors make contact with the mating connectors of the VXI backplane, the injection/ejection mechanism is rotated so that the injection protrusion is forced against an injection lip on the card guide rail. This action essentially pulls the plug-in forward so that the connectors of the plug-in and the VXI backplane mate and are in a friction fit relationship. During removal of the plug-in, the injection/ejection mechanism is rotated in an opposite manner so that the ejection protrusion is forced against an end of the card guide rail. This action essentially pushes the plug-in backwards so that the connectors of the plug-in and the VXI backplane are no longer in a mating and friction fit relationship.
Yet another aspect of the invention is to provide the capability of making new decoding routines available to the controller card so that the controller card is capable of communicating with new designed VXI product modules without the need for revised firmware. In order to accomplish this objective, a VXI product plug-in module is provided with descriptor data and program routines stored on a local memory, preferably an electrically programmable read only memory (EPROM) or the like, that can be uploaded to and executed by a processor on the controller card so that the controller card has the necessary information for communicating with the module. Upon system start-up, the controller card uploads the descriptor data and program routines stored in the local memory of the module and stores it preferably in a random access memory (RAM). The processor on the controller card can then refer to the descriptor data and execute the uploaded program routines in order to issue proper addressing and operating instructions for the new module.
Yet another aspect of the invention is to provide an emergency reset mechanism for a switching module that allows a user to open all the switching relays in the module by simply operating an externally provided switch. This is of value when a hazard condition exists that requires the user to quickly respond to a hazardous condition. The emergency reset mechanism can control the opening of the switches within a single module, without opening the switches in other modules or plug-ins. This allows for other test and diagnostic procedures to run on other modules, even though an emergency condition has occurred. The module also includes a jumper that when set, couples the emergency reset mechanism of one module to the other modules sharing the local bus (LBUS) of the VXI backplane bus to open all the switches on all modules.